I gave DOT 5 a try in the '55, all new hydraulics-wheel ctls, master, and lines. Bleeding was no problem, and the brakes worked great. Then one day I noticed a small puddle under the truck. I cleaned it up cause I didn't really see anywhere that it could be from. Well, it came back. I kept an eye on it for a while to see what it could be. Turned ou to be the master cylinder, the front wheel cylinders were leaking slightly as well. I called the manufacturer and explained the situation. I was informed that DOT 5 is not compatible with most brake components. I had also seen an article by Bob Adler in Vintage Truck on the same subject, he had also suggested not using DOT 5, unless it was called for as OE. After flushing the system, I put DOT 3 in and have had no problems since. If you plan on driving the truck regularly, stick with DOT 3. That's what it calls for, you'll avoid many hassels using that.
